The invention concerns networks which offer services to registered users. For example, in the IP Multimedia (IM) Subsystem as defined by the 3rd Generation Partnership Project (3GPP), it is necessary for an UE to be registered before the UE can make use of the multimedia services.
Thus, in case the user (i.e., UE) does not send a register request (e.g., a SIP (Session Initiation Protocol) REGISTER message) first, the network is not able to handle service requests from that user, which leads to a failure. In turn, the user is not notified about the failure and, hence, is not able to identify the reason for the failure, i.e., the non-acceptance of the service request.
Moreover, in a 3GPP environment, the network can initiate a Network Initiated De-registration. This is performed, for example, in order to avoid problems in the servers. The user may or may not be notified about the action, depending on whether he is previously subscribed to be notified and it is reachable or not.
If the user has been de-registered from the network but he was not notified because of one of the above listed reasons, he may anytime send a session initiation request to the network. If that is the case, the network can not serve the user since it is not registered. However, also in this case the user is not aware of the fact that he is no longer registered.
Thus, the above situations lead to the problem that a user can not be served and that the user is not aware why the network does not accept his service request.